Plastic injection molding cartridge



Patented Feb.` 10, 1942 PLASTIC INJECTION MOLDING CARTRIDGE George W.Wacker, Cincinnati, Ohio, assignor to The Grotelite Company, Bellevue,Ky., a corporation of Kentucky Original application August 16, 1938,Serial No. 225,181. Divided and this application April 21, 1939, SerialNo. 269,224

1 Claim.

My invention relates to a package or cartridge which is filled with aplastic extrusion material for use in an injection machine adapted toeject chine so that the use of plastic materials in loose powder orgranular form may be eliminated and so that the accuracy of measurementof the in- Ajected material may be increased with a constant decrease ofthe plastic material waste.

It is a further object of my invention to provide a cartridge that canbe preheated so that it can be inserted in the plastic injection machinein its heated condition.

It is a further object of my invention to provide such a cartridge thatthe molding material therein may be preheated to molding temperatureexteriorly of the injection machine without injury to the material.

A more particular objectof this invention is to load a cartridge bypouring or .forcing plastic material into the cartridge and thereafterpreferably hermetically sealing the cartridge.

It is an object of my invention to eliminate the process of grinding theplastic material and to eliminate the subsequent use of such groundmaterial which has to be fed to a plastic machine in granular form andheated as it is fed. This results in an irregular feeding, a diiiicultheating and a slowing down of the production of the machine .due to thenecessity of preheating each granular charge. The granular charge sticksin the machine, making it difcult to feed uniform amounts and iswasteful in its handling.

By this invention, I use the rigid or semi-rigid plastic material whichis poured directly into a cartridge and is sealed therein. It can thenbe preheated while still in its solid condition and ejected as set forthin the application of George W. Wacker, Serial No. 195,591, filed March12, 1938.

This application is a division of my copending application, Serial No.225,181, led August 16, 1938.

Referring to the drawing:

Figure 1 is a diagrammatic view of the several steps of the invention.

Figure 2 is a diagram of the apparatus used to effect the steps of theprocess. v

Figure 3 is a section through a cartridge having a load of solid plasticmaterial with which it has been filled while the plastic is in itsliquid or semi-liquid condition.

, nature or requiring very high pressure to force (Cl. 20G-56) Referringto the drawing in detail, the first step in the process is tomanufacture the plastic in the container I (or by any conventionalmeans), and after the completion of its manufacture while it is still inits liquidor semi-liquid, or plastic, state, it is poured, as the secondstep, into the cartridge 2. Then it is immediately sealed, as step 3, bythe cover 3 being applied to the cartridge 2. Any one ofthe types ofcartridge shown in the above mentioned Wacker application Ser. No.195,591 may be employed.

Thereafter as step 4, it is cooled and ready for storage or shipment.When it is ready for use, the solid plastic within the sealed cartridgeis heated. This is step 5.

The temperature can gradually be brought up until the plastic is againsufliciently plastic due to heat, but without oxidation, to be ejectedfrom the cartridge when it is loaded in the injection machine. It isthen loaded in the injection machine, step 6, and ejected by applyingpressure to one end and forcing the material through a rupturedcontainer or cartridge at the other end. This is step '1. v

It is therefore seen that my method comprises l the steps of making theplastic in liquid or s'em'iliquid condition, pouring it in suchcondition into a container, such as a cartridge, sealing it, cooling it,reheating it while 'sealed and thereafter immediately placing it inheated condition in the ejection machine.

I find that this is desirable with certain types of plastics inpreference to lling the cartridge with granular plastics. 'A muchsmaller cartridge can be employed. A far more accurate quantity can bemeasured. The size of the cartridge can be reduced thereby reducing thesize of the machine and the bulk of the cartridges in shipping. Theheating problem without oxidation is successfully solved.

In handling certain materials, such 'as styrene, Lucite and similarcompounds of very friable into the mold, much diiculty has beenexperienced due to some of the material being forced into the clearancespace between the plunger and its cylinder wall, resulting in a stuckplunger.

An extremely close t between the cylinder and plunger, with thepractical elimination of running clearance, so that no space exists forthe material to crowd in, results, in practice, in gouged cylinders dueto mechanical friction, unless-very hard and costly materials areemployed. Some improvement might be obtained by allowing an excessiveclearance between plunger and cylinder,

resulting in a comparatively thick skin of leaking material. Dilculty inkeeping the plunger central, with a uniform wall of leaking materialseparating it from the cylinder wall, precludes the use of this methodin practice. The cartridge system overcomes these difficulties.

By the use of the cartridge system, the act of collapsing the cartridgeupon its contents under very heavy pressure, has the additional verydesirable eiect of forcing the material of the cartridge into closecontact with the sides of the cylinder. This contact Iis closer. thanpossible with a running fit between piston and cylinder, and preventsthe material from finding its way into this space and jamming. As thecrushed cartridge is expelled at the end of the stroke, this operationconsists virtually of fitting a very tight tting seal between the end ofthe plunger and the actual material to be extruded, because not only isthe clearance space sealed, but the material of the cartridge isinterposed between the molding material and the end of the plunger. Inthis way, molding materials that give much trouble with ordinaryself-heating molding machines are readily handled by the cartridgemethod.

With ordinary self-heating injection molding machines, a substantialportion of the working stroke of the injection plunger is used forfeeding a fresh charge of material into the h'eating cylinder, and theeffective stroke forcing the plasticized material into the mold at highpressure, does not commence until this feeding of new material has beenaccomplished.

By using the cartridge system, practically the entire stroke of theinjection plunger is made effective, and is utilized for the injectionof material into the mold. The only portions of the stroke not utilizedfor useful work are the slight clearance provided to assure properentrance of the cartridge into lthe cylinder, and such part of thestroke as is necessary to eject the exhausted cartridge. Therefore, amachine using the cartridge method has a capacity from two to threetimes as great as the conventional type.

In comiection with the above, it should also be observed that theconventional type of machine, using material in loose powder form, mustlose some of the plunger travel in compressing this loose material tothe point where th'e great pressure of the plunger may be transmittedthrough the new charge, to the plasticized charge awaiting transfer tothe mold.

The conventional type of molding machine uses molding powder that hasbeen ground to a certain size of particle. By the use of the cartridgemethod, the necessity of converting the manufactured stock into a powderof certain size is eliminated, and the stock may be inserted intosuitable cartridges or containers during the process of manufacture. Inthis way a substantial saving in production cost is effected.

Another advantage lies in the fact that gates and sprues may be packedinto the cartridges, together with enough other material to make therequired weight, Without the necessity of cutting them up or grindingthem into a powder.

By filling cartridges with dense material during the process ofmanufacturing the molding compounds, instead of using the material inthe powdered form, an increase of almost one hundred per cent in volumeis obtained. The proportion of loose to compressed material isapproximately 2.5 to 1, but allowance must be made for some space lossin filling and for the material of the cartridge.

The conventional type of molding machine, with its self containedheater, possesses an inherent fault in that the temperature of theheating element must obviously be higher than the plasticizingtemperature of the material. This temperature differential depends uponmany factors, but it Will be readily seen that a temporary delay in theoperation of the machine, resulting in subjecting the material in theheating charnber to this higher temperature for a period longer thannormal, will also result in overheating of the charge, causing bleedingor oozing of the material from the open end of the chamber. To minimizethe effects of this bleeding," it is customary to provide the injectionnozzle with a comparatively small orifice, thereby interposing someresistance to this bleeding, and reducing it to within practical limits.This small orifice, or restriction, necessarily limits the passage ofthe plasticized material into the mold, and slows up the injectionprocess in proportion to the restriction.'

By using the cartridge principle, there is no heating element to be keptat a temperature higher than that of the cartridge when it is placed inthe machine. Therefore, there is no necessity for the restricted nozzleessential to the operation of the conventional machines, and the orificecan be of such size as will permit the injection of the material intoth'e mold in the shortest possible time, or with a greatly reducedpressure.

In considering the above, it must be recalled that the cartridge may beof such size as to require its entire contents to fill the mold. Or itmay contain enough plasticized material to permit filling the mold manytimes before becoming emptied. In either case, the large nozzle orificemay be used.

It will be understood that I desire to comprehend within my inventionsuch modifications as may be necessary to adapt it to varying conditionsand uses.

Having thus fully described my invention, what I claim as new and desireto secure by Letters Patent, is:

A package comprising a cartridge containing a thermosetting moldingmaterial, said cartridge being indestructible when heated to atemperature at which the molding material can be injection molded, saidcartridge comprising a case ing of uniform cross-section havinghermetically sealed ends, one of said ends being constructed andarranged to permit rupture thereof upon the application of injectionpressure upon the opposite end to permit ejection of the moldingmaterial from the cartridge, said opposite end forming a plunger forforcing the contents through said rupturable end.

GEORGE W. WACKER.

